1. Field of the Invention
The present invention relates to an ink jet print head that ejects ink onto a print medium to perform printing.
2. Description of the Related Art
Ink jet printing systems are in wide use today not only due to their ability to print highly defined images at high speeds, but also due to their ability to perform printing on even a print medium not subjected to special treatments. Ink jet print heads that actualize these ink jet printing systems have various types of ejection systems, which are typified by the use of the energy of heat-generated bubbles to eject ink, or the use of piezoelectric elements.
In recent years, with respect to such ink jet print heads, there has been a growing demand for higher print quality and faster printing speed. Means that have been proposed to increase the printing speed include increasing the number of nozzles in the ink jet print head and improving the ejection frequency.
One of the factors that determines the upper limit of the ejection frequency of an ink jet print head is the time it takes for a nozzle, after ejecting ink, to be supplied and filled with ink again (also referred to as refill time). The shorter this refill time becomes, the higher the ejection frequency will be at which the printing can be performed.
FIG. 11 is a partially cut-away cross section view showing the interior of a conventional print head. In a conventional nozzle structure, which supplies ink from a single ink supply port 95 opening along arrays of nozzles through only one ink path 97 into pressure chambers 96, the refill time is dictated by the flow resistance of the ink flow path. As a means to reduce the refill time, Japanese Patent Laid-Open No. H10-181021 (1998) discloses a technique that arranges flow path walls so as to form a plurality of flow paths in each of the pressure chambers, thereby increasing the number of ink inflow paths.
To obtain highly defined, deep-grayscale, high-quality printed images, there are currently demands for an ink jet print head which has low variation in the ejection volume of any particular nozzle, and low variation among the different nozzles in the print head. Regarding ink jet print heads that eject ink via the force of an expanding bubble, however, the amount of ink ejected changes with the temperature near the ejection opening. Particularly when there is a local temperature distribution within the nozzle array, the ink ejection volume varies according to the temperature distribution, resulting in a printed image having density variations and therefore a degraded image quality. Although, to deal with this situation, a variety of measures have been taken on the ink jet printing apparatus body side, such as multi-path techniques and drive pulse control, the stabilization of the ink ejection volume depends largely on the stand alone performance of the ink jet print head.
Japanese Patent Laid-Open No. H10-157116 (1998) discloses a technique to reduce printing variations that makes the temperature near the end of the print head and the temperature near the central portion thereof almost equal by the provision of heat dissipating fins at the center of the print head.
To minimize image quality degradations caused by an increase in temperature distribution of an ink jet print head, Japanese Patent Laid-Open No. 2003-170597 discloses a technique that introduces a heat conductive film into a print head board and connects it to a heat dissipating portion that dissipates heat to the ink, thereby suppressing the overall temperature rise. Japanese Patent Laid-Open No. 2003-118124 discloses a technique that cools the print head board itself via an ink flow supplied to the print head.
The conventional ink jet print head has a single ink supply port opening along the nozzle arrays, as shown in FIG. 11. In this configuration, pressure generated in the pressure chamber 96 by an expanding bubble escapes toward the ink path 97, with the result that the generated pressure may not be fully utilized for ink ejection. Since the pressure escapes toward the ink path 97, the ejected ink may stray from the intended direction.
Further, in the conventional configuration, heat generated by a heating resistor is transmitted through the print head board and dissipated outside the nozzle arrays. This is because the portion where the ink supply port is provided constitutes a heat insulating portion, allowing the heat generated by the heating resistor only to escape toward the outside of the nozzle arrays. This configuration makes it difficult for heat to escape. A local temperature rise in the print head board may be reduced by widening the interval between the heating resistors to increase the heat escape path. In that case, the print head board becomes large in size.